Explanation:
The sulfonation of the naphthalene yield 2 products under different conditions:
When the reaction is carried at 80 °C, 1-naphthalenesulfonic acid is the major product because it is kinetically favoured product as arenium ion formed in the transition state corresponding to 1-naphthalenesulfonic acid is more stable due to better resonance stabilization.
When the reaction is carried at 160 °C, 2-naphthalenesulfonic acid is the major product as it is more stable than 1-naphthalenesulfonic acid because of steric interaction of the sulfonic acid group in 1-position and the hydrogen in 8-position.
The products are shown in image below.
